(1) Technical Field
The invention relates to a manufacturing method for hollow components using a tubular film and a mould.
(2) Description of Related Art
Hollow components, particularly those used in the aerospace industry, such as door elements on helicopters, are often manufactured in the manner described above. In this context, a mould usually consists of at least two complementary, bowl-shaped tool parts, into which a plastic material is fed for shaping. The tubular film is placed in one of the tool parts that has been covered with a base material before it is sealed off into a hollow body with the second or additional tool parts. Plastic materials include both materials consisting entirely of plastic and composite materials containing plastics, particularly fibres that contain plastics. The steps a) and b) of feeding and conforming the plastic working material are usually carried out before steps c) to d). However, injection methods are also known in which a hot, flowable material including a plastic is injected into a mould in which the tubular film has been fed and possibly expanded, between the outer surface of the tubular film and the inner surface of the mould.
For reasons of cost, a tubular film with a cross section that is adaptable thereto is not normally used even for hollow parts, for example with variable cross sections, or in components having complex hollow part geometry, instead a tube with constant cross section is used. Accordingly, the tube must be capable of expanding variably to ensure that pressure is applied to the material evenly, including in component corners that are difficult to reach. Problems can arise particularly in these zones: it is possible that the yield strength of the tubular film used may be exceeded, so that it is no longer possible to exert sufficient compression on the work materials. Ultimately, further expansion may cause the tubular film to tear. In both cases, the result is a rejected component, which is expensive.
Previously, this problem has been addressed essentially by using a somewhat oversized tube with a simple fold, usually into a Z shape. Even so, complex components constantly suffer from inadequate compression of the materials or overexpansion of the tube.
The document JP 58008616 A discloses a method how to perform molding with fidelity to a mold, by inserting a freely expandable hollow tubular member shaped with an elastic material into a tubular member having a concave part and a cross-sectional shape except a circular shape, then placing it in a mold, expanding the hollow tubular member, heating the tubular member and adapting it to a shape of the mold. By doing so, flash in the mold does not generate at a curved part and molding can be done according to the mold.
The document DE 102006031335 A1 discloses a process to manufacture an aircraft fuselage stringer in composite material, a form core has a hollow profile with longitudinally segmented folding sides. The form core is converted as required from open to closed (A) presentation for carbon fiber layup. On completion of the fiber and resin layup process, the material and form core are subject to heat and pressure for the duration of the curing process. The form core sides have interlocking profiles defining the external shape of the closed unit. The closed unit is retained in the closed presentation e.g. by welding. The form core is a plastic extrusion.
The document U.S. Pat. No. 5,129,813 A discloses a vacuum bag including a non-porous material having impressed therein a three-dimensional pattern which defines a plurality of interconnected channels, methods for producing the vacuum bag, molding methods using the vacuum bag, and improved composite articles produced by the molding method.
The document US 2003104156 A1 discloses a composite material, which can be used as an alternative material to a prepreg, comprising a dry substrate fabric sheet, and at least a thermosetting resin thin film being attached to one of the surface of the substrate fabric sheet. The substrate fabric sheet is thick and a multi-axial laminate structure formed by laying up a plurality of aligned fiber plies, and is not impregnated with resin previously.
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